The observation group had similarly high rates of suppression to less than 400 copies per milliliter (94% at birth and 95% throughout the breast-feeding period). The rate of suppression of HIV-1 RNA to less than 50 copies per milliliter differed significantly between the NRTI group and the proteasei nhibitor group at delivery (81% and 69%, respectively; 95% CI for percentage-point difference, 4 to 20) but not during breast-feeding (83% and 77%, respectively; 95% CI for percentage-point difference, −3 to 14). The rate of suppression to less than 50 copies per milliliter in the observational group was 77% at delivery and 84% throughout the breast-feeding period.